Auxiliary power units (“APU”) are used in aircraft to provide electrical power and compressed air to various aircraft systems and components. When an aircraft is on the ground, its main source of electrical power and cabin conditioning comes from the APU. In particular, the APU can power the environmental control systems, air drive hydraulic pumps, and the starters for the engines. When an aircraft is in flight, the APU may provide pneumatic and/or electric power to the aircraft.
Typically, APUs are located in the aft section of the aircraft, at or near the tailcone section and include inlet and exhaust ducting that exit through an opening, or cut-out, in the aircraft fuselage to allow sufficient air flow through to the APU. For aircraft on which APUs operate during flight, a RAM air door is typically provided to protect the APU from foreign object damage when not in use and/or during ground movement, and to maximize airflow into the APU when performance or oil cooling at altitude is required. Thus, when the APU is running, the RAM air door opens, either on the ground or in flight. Typically in such configuration, the RAM air door is configured to open approximately 20-45 degrees during a flight phase of operation and in many cases approximately 70 degrees, or fully open, such as during a ground phase of operation full open (70 degrees) on ground, relative to the aircraft fuselage. This allows for noise reduction on the ground, while optimizing RAM recover for the APU performance in flight with minimal drag to the aircraft.
In many conventional aircraft types, the actuation of the RAM air door is achieved by mounting an actuating device proximate the RAM air door. In most instances, the actuator is mounted to an interior surface of the inlet duct and coupled to the side or front of the inlet door. The positioning and mounting location of the actuator may affect aerodynamic performance of the door and may affect acoustic treatment performance of the inlet duct. In many instances, the actuator, and more particularly the actuator rod, may extend into the flow of air in the inlet duct disrupting the aerodynamic performance. In addition, the mounting location of the actuator may impact accessibility of the actuator for maintenance, repair and replacement purposes.
Therefore, there is a need for a RAM air door actuator that minimizes disruption to the aerodynamic performance of the RAM air inlet door to which it is coupled and minimizes acoustic treatment performance on the inlet duct. In addition, there is a need for a RAM air door actuator that provides maintenance access from inside the APU compartment for the purpose of repairing and/or replacing the actuator. The present invention addresses one or more of these needs.